Plastic film of, for example, polyethylene or polypropylene is virtually impossible to tear directly along a straight or other regular line. This is due to the fact that two forces, when applied in opposite directions in shear or tension over an area of such a film or thin sheet, can cause the plastic film material to deform and stretch plastically until its elastic limit is passed, whereupon a tear or separation starts. Such a tear can begin anywhere in the deformed, stretched area--which is usually at the weakest point produced by the above-described thickness reduction--and will not, in general, run normal to the tearing forces being applied. Thus, even with evenly and carefully applied forces, it is not likely that a person will be able to tear a plastic film along a preselected straight or other regular line due to the stretchability of the film.
As a result of this, in order to open a plastic pouch, it is often necessary to employ a sharp tool or other instrument. The need for a separate cutting tool is obviously bothersome, and often such tools are not available.
One solution to the above problem has been to perforate or score a prescribed portion of the pouch or film. This allows for reasonably regular tearing of the plastic film material, but the film itself is weakened. Further, perforations and the like tend to weaken the desired seal, can thus cause leakage in a pouch containing a fluid, and may thus limit the practical utility of the pouch.
In a sealed plastic pouch for containment of a fluid and having a spout for discharge of such a fluid, it would be desirable that such spout be readily openable without the use of tools or the need for scoring the plastic material.